Expandable member for an electrophysiology catheter

ABSTRACT

Expandable electrophysiology catheters having electrodes mounted on splines of an expandable member are described. The splines of the expandable member include subsegments between a proximal location and a distal intersection at a central axis. The subsegments can include respective top-down profiles, and at least one of the top-down subsegment profiles is straight between the central axis and an adjacent top-down subsegment profile. The subsegments can be interconnected to extend continuously about the central axis from the proximal location to the distal intersection. Other embodiments are also described.

This application is a continuation of U.S. patent application Ser. No.15/867,657 filed on Jan. 10, 2018, which claims the benefit of priorityof U.S. Provisional Patent Application No. 62/445,137, filed Jan. 11,2017, and these applications are specifically incorporated by referenceherein in their entirety.

BACKGROUND Field

Embodiments are related to electrophysiology (EP) catheters. Moreparticularly, embodiments are related to EP catheters having electrodesmounted on flexible spine assemblies to detect cardiac rhythm disorders.

Background Information

Heart rhythm disorders are common in the United States, and aresignificant causes of morbidity, lost days from work, and death. Heartrhythm disorders exist in many forms, of which the most complex anddifficult to treat are atrial fibrillation, ventricular tachycardia, andventricular fibrillation. Other rhythm disorders may be easier to treat,but may also be clinically significant, including supraventriculartachycardia, atrial tachycardia, atrial flutter, premature atrialcomplexes/beats, and premature ventricular complexes/beats. As a resultof these cardiac electrical impulse abnormalities, the heart may not beable to expel blood properly, and the blood may pool and clot. A bloodclot can move to a peripheral artery or vein, e.g., a neurovessel, and astroke can result.

Definitive diagnosis of cardiac electrical impulse abnormalities hasbeen performed using electrode-bearing electrophysiology (EP) cathetersplaced within the heart chambers. EP catheters typically includeelectrodes positioned along a catheter shaft or an expandable basket tomap the electrical activity within a heart chamber. Expandable basketstypically have proximal and distal ends, and include several spinesconnected at the proximal and distal ends. Each spine can have at leastone electrode. Various electrode designs are known, including singlecurvilinear, lasso-shaped, and multi-branched arrangements. The spinesmay be expanded to bow radially outward against a wall of the heartchamber, and the electrodes can contact and sense electrical activitywithin the chamber wall. Typically, the bowed spines are axiallyoriented and have arc-shaped side profiles between the proximal anddistal ends of the expandable basket.

SUMMARY

Existing electrophysiology (EP) catheters do not provide a complete andstable map of electrical activity within a heart chamber. The shape ofthe heart chambers, e.g., atria, can vary substantially during thebeating of the heart. The expandable baskets of existing EP cathetersmay not provide adequate electrode coverage and/or may not conform tothe irregular shape of the atria. More particularly, when expandablebaskets of existing EP catheters are deployed, spline elements of themembers tend to expand unevenly and do not provide adequate coverage ofthe target anatomy. Thus, electrodes mounted on the splines may beunevenly distributed within the target anatomy. Uneven distribution ofthe electrodes can cause incomplete and/or faulty electrograms.

In an embodiment, an expandable member of an EP catheter is provided.The expandable member includes several splines, and each spline hasseveral subsegments extending between a proximal location at a centralaxis and a distal intersection at the central axis. At least one of thesubsegments has a top-down profile extending straight between thecentral axis and another subsegment. For example, a distal subsegmentmay extend from the distal intersection to a medial subsegment. Themedial subsegment may curve around the central axis toward the proximallocation. Accordingly, a distal portion of the expandable member may beradially oriented along a transverse plane, and the medial portion ofthe expandable member may spiral around the central axis to support theexpandable member within a target anatomy.

In an embodiment, the expandable member includes subsegments havingstraight top-down profiles at both the distal intersection and theproximal location. The distal and proximal subsegments, however, mayextend from the central axis to the medial arcuate subsegment indifferent radial directions. For example, the distal subsegment mayextend from the central axis in a first radial direction and theproximal subsegment may extend from the central axis in a second radialdirection offset from the first radial direction by an angle in a rangeof 90-175°. A structural stability of the expandable member and adistribution of electrodes mounted on the spline can be controlled byadjusting the offset angle of the distal and proximal subsegments.

In an embodiment, a distal subsegment of the expandable member includesa concavity that transitions during deployment. For example, the distalintersection of the spline may be an apex of the concavity, and the apexmay transition from being a distalmost location on the spline in anundeployed state, to being proximal to a distalmost location on thespline in a deployed state. Accordingly, the distal intersection may beoffset from an endocardium after deployment to reduce a risk of tissuedamage.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the Detailed Description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an electrophysiology (EP) catheter system, inaccordance with an embodiment.

FIG. 2 is a side view of an expandable member in an undeployed state, inaccordance with an embodiment.

FIG. 3 is a side view of an expandable member in a deployed state, inaccordance with an embodiment.

FIG. 4 is a perspective view of an expandable member in a deployedstate, in accordance with an embodiment.

FIG. 5 is a cross-sectional view, taken about line A-A of FIG. 3, ofseveral splines of an expandable member symmetrically arranged about acentral axis, in accordance with an embodiment.

FIG. 6 is a cross-sectional view, taken about line B-B of FIG. 3, ofseveral splines of an expandable member symmetrically arranged about acentral axis, in accordance with an embodiment.

FIGS. 7A-7D are top views, which reveal a top-down profile of a singlespline of an expandable member exhibiting different degrees of twistabout a central axis, in accordance with several embodiments.

FIG. 8 is a perspective view of a spline of an expandable memberexhibiting a twist about a central axis, in accordance with anembodiment.

FIG. 9 is a side view of a spline of an expandable member exhibiting atwist about a central axis, in accordance with an embodiment.

FIG. 10 is a side view, which reveals a side profile of a distal portionof an expanded spline of an expandable member, in accordance with anembodiment.

FIG. 11 is a side view of a distal portion of an unexpanded spline of anexpandable member, in accordance with an embodiment.

FIG. 12 is a side view of a spline of an expandable member havingportions of varying radiopacity, in accordance with an embodiment.

FIG. 13 is a cross-sectional view, taken about line C-C of FIG. 12, of aspline of an expandable member, in accordance with an embodiment.

FIG. 14 is a perspective view of an outer envelope of an expandablemember, in accordance with an embodiment.

DETAILED DESCRIPTION

Various embodiments and aspects of the invention will be described withreference to details discussed below, and the accompanying drawings willillustrate the various embodiments. The following description anddrawings are illustrative of the invention and are not to be construedas limiting the invention. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentinvention. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present invention.

Reference in the specification to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin conjunction with the embodiment can be included in at least oneembodiment of the invention. The appearances of the phrase “in oneembodiment” in various places in the specification do not necessarilyall refer to the same embodiment. Although the processes depicted in thefigures that follow may be described below in terms of some sequentialoperations, it should be appreciated that some of the operationsdescribed can be performed in a different order. Moreover, someoperations can be performed in parallel rather than sequentially.

In an aspect, an electrophysiology (EP) catheter having an expandablemember to map a target anatomy, e.g., a heart chamber such a ventricleor an atrium, includes a spline having several subsegments extendingabout a central axis. The spline includes several subsegments that, whenviewed in a top-down direction, include straight profiles extendingradially from the central axis and arcuate profiles twisting around thecentral axis. The arcuate profiles may extend continuously from thestraight profile such that ends of the arcuate profiles are supported byends of the straight profiles. Thus, the straight profiles, when viewedfrom above, may be separated by an angle. The twisting structure of theexpandable member can provide structural resilience and stability, and aspacing and distribution of electrodes mounted on the spline may remainuniform when deployed within the atrium. For example, the distributionof the electrodes over an envelope outlined by the opened expandablemember may be more or less even based on the angle between the straightprofiles. The angle can also control the degree of opening and closingof the expandable member. For example, the amount of opening of theexpandable member may be inversely proportional to the angle between thestraight profiles. Similarly, the angle between the straight profilesmay also affect the ease of opening and closing of the expandablemember. For example, the ease of opening of the basket may be inverselyproportional to the angle between the straight profiles. Accordingly,the EP catheter can produce stable, complete, and accurate electrogramsof the atrial endocardium.

Referring to FIG. 1, a side view of an electrophysiology catheter systemis shown in accordance with an embodiment. An EP catheter system 100includes an EP catheter 102 having an expandable member 104 connected toa catheter shaft 106. In an embodiment, EP catheter system 100 includesa handle 108 connected to catheter shaft 106. For example, cathetershaft 106 may extend along a central axis 110 between a proximal end 112and a distal end 114, and handle 108 may be attached to proximal end112. Handle 108 can provide an interface between a physician and EPcatheter 102. Handle 108 may also provide an interface betweencomponents of EP catheter system 100 and external components. Forexample, handle 108 may include an integral connector (not shown) toconnect with an electrocardiogram (ECG) data recording system through adata cable.

In an embodiment, handle 108 is connected to expandable member 104through catheter shaft 106 to allow the physician control movement ofexpandable member 104 by manipulating handle 108. Expandable member 104may be joined to a distal end of the catheter shaft 106, e.g., bybonding, potting, or otherwise joining splines of expandable member 104to catheter shaft 106 at distal end 114.

Referring to FIG. 2, a side view of an expandable member in anundeployed state is shown in accordance with an embodiment. In anundeployed state 200, expandable member 104 may be constrained within aninner lumen of an introducer or guide catheter 201. Introducer or guidecatheter 201 may be advanced over expandable member 104 to force theexpandable member into a collapsed state. In the collapsed state,expandable member 104 can be advanced into or retracted from the targetanatomy.

Expandable member 104 may include one or more splines 202, and thus, aspline 202 may be constrained within the inner lumen. In undeployedstate 200, the flexible splines 202 may be arranged in a compressedlinear axial orientation. For example, spline 202 may extend between apair of proximal locations, e.g., a first proximal location 204 and asecond proximal location 206 toward a distal tip. The distal tip ofspline 202 may be at an intersection between spline 202 and central axis110. More particularly, a location on spline 202 at the intersection ofspline 202 and central axis 110 may be referred to as a distalintersection 208. Thus, in undeployed state 200, spline 202 may extendfrom first proximal location 204 within catheter shaft 106 to secondproximal location 206 within catheter shaft 106 along a path thatextends forward to distal intersection 208 and then returns backward tosecond proximal location 206.

In an embodiment, the proximal locations of spline 202 are connected tocatheter shaft 106 at distal end 114. That is, splines 202 may be bondedto catheter shaft 106 by an adhesive or solder joint 220. Joint 220 maysecure expandable member 104 to catheter shaft 106 to transmitadvancement and retraction forces from handle 108 to expandable member104 through catheter shaft 106. In an embodiment, when expandable member104 is in a deployed state (FIG. 3), a joint 220 between expandablemember 104 and catheter shaft 106 may be located within 1-2 cm of distalend 114 of catheter shaft 106. More particularly, the joint betweenspline 202 and catheter shaft 106 may be within an inner lumen ofcathether shaft 106 proximal to distal end 114.

Referring to FIG. 3, a side view of an expandable member in a deployedstate is shown in accordance with an embodiment. Expandable member 104may be advanced from introducer 201 to expand from undeployed state 200to a deployed state 302. For example, handle 108 may be actuated toadvance the pair of proximal locations 204, 206 within the inner lumenof introducer 201 until distal end 114 is distal to a respective distalend of introducer 201. First proximal location 204 and second proximallocation 206 on spline 202 may be collocated at distal end 114 ofcatheter shaft 106. That is, spline 202 may extend unconstrained fromfirst proximal location 204 at distal end 114 to second proximallocation 206 at distal end 114.

In deployed state 302, expandable member 104 may have an outer envelopein a shape of a sphere, an ellipsoid, or another bulbous volumetricshape. More particularly, the expanded splines 202 of expandable member104 may form an outer envelope in deployed state 302, and the outerenvelope may approximate a volume of a target anatomy, e.g., a heartatrium. The bulbous volumetric shape of expandable member 104 may have adistal surface that extends transverse to central axis 110. As describedbelow, spline 202 may extend in a transverse direction 306 at distalintersection 208. That is, central axis 110 may be orthogonal to theouter envelope of expandable member 104 at distal intersection 208 indeployed state 302, as defined by splines 202 passing laterally throughdistal intersection 208 in transverse direction 306. Thus, the outerenvelope of deployed expandable member 104 can be a sphere havingflattened or concave poles at a proximal and/or distal end.

Each spline 202 of expandable member 104 may include an electrode 304.For example, electrodes 304 may be mounted on splines 202 such thatelectrodes 304 contact the target anatomy in deployed state 302. In anembodiment, electrodes 304 are on flex circuits that are wrapped over anouter surface of spline 202 to achieve endocardial contact on eitherside of spline 202, or around half of a circumference of the outersurface of spline 202. Electrodes 304 on splines 202 may be referencedagainst other electrodes to generate an electrical signal. By way ofexample, a reference electrode 308 may be mounted on catheter shaft 106.Alternatively, reference electrode 308 may be mounted on a surface ofspline 202 that does not contact endocardial tissue during deployment ofexpandable member 104. For example, reference electrode 308 may be on aninner surface of spline 202. A voltage differential between electrode304 on a surface of spline 202 facing a target anatomy and referenceelectrode 308 may be monitored to determine electrical activity in thetarget anatomy. Accordingly, electrodes on splines 202 may be used tomap the atrium.

Referring to FIG. 4, a perspective view of an expandable member in adeployed state is shown in accordance with an embodiment. Each spline202 may extend continuously from first proximal location 204 at distalend 114 of catheter shaft 106 to second proximal location 206 at distalend 114. A single spline 202 may extend between the pair of proximallocations, and the single spline 202 may intersect central axis 110 atdistal intersection 208. Accordingly, the single spline 202 may extendin transverse direction 306 through central axis 110 to transition froma first spline segment 402 to a second spline segment 404. That is,first spline segment 402 may extend between first proximal location 204and distal intersection 208, and second spline segment 404 may extendbetween second proximal location 206 and distal intersection 208.

The splines 202 of expandable member 104 may overlap each other atdistal intersection 208 (FIG. 6). That is, each spline 202 may crosscentral axis 110 at distal intersection 208 in a respective transversedirection 306. The transverse directions 306 may be within a sametransverse plane, however, and the transverse plane may be orthogonal tocentral axis 110. Accordingly, the overlapping splines 202 may form atransverse envelope surface at distal intersection 208. The transverseenvelope surface may be a flattened pole of a spherical envelope.

In an embodiment, the splines 202 are not constrained relative to eachother at distal intersection 208, and thus, splines 202 may slide overeach other at distal intersection 208. The floating tip and the relativemovement of splines 202 at distal intersection 208 can prevent bindingor uneven collapse of the struts during retraction of expandable member104 into an introducer or guide sheath 201. For example, as the splines202 collapse, they can slide over each other, which may prevent theexpandable member 104 from reducing in size in a lopsided or asymmetricmanner. Alternatively, a coupling, such as a distal cap, a string orwire winding, or another fastener may bind splines 202 together toconstrain relative movement between splines 202 at distal intersection208.

Referring to FIG. 5, a cross-sectional view, taken about line A-A ofFIG. 3, of several splines of an expandable member symmetricallyarranged about a central axis is shown in accordance with an embodiment.In an embodiment, expandable member 104 includes several splines 202symmetrically disposed about central axis 110. Splines 202 can besymmetrically arranged about central axis 110 when a top-down profile ofexpandable member 104 has splines 202 bisected by a longitudinal plane502. Central axis 110 may extend within longitudinal plane 502. Thus,longitudinal plane 502 may be orthogonal to a transverse surface of theouter envelope of expandable member 104 in deployed state 302. Aprojection of each spline 202 onto a transverse plane orthogonal to thecentral axis 110 (and longitudinal plane 502) may include first splinesegment 402 on a first side 504 of longitudinal plane 502, and secondspline segment 404 on a second side 506 of longitudinal plane 502, i.e.,on an opposite side of longitudinal plane 502. First spline segment 402may extend radially outward from central axis 110 on first side 504 oflongitudinal plane 502, and second spline segment 404 may extendradially outward from central axis 110 on second side 506 oflongitudinal plane 502.

An overall diameter 508 of expandable member 104 may be measured betweenlateral maxima of expandable member 104. More particularly, a locationon first spline segment 402 at a maximum radial distance from centralaxis 110 may be a first radial limit 510, and a location on secondspline segment 404 at a maximum radial distance from central axis 110may be a second radial limit 512. The radial distance between firstradial maximum or limit 510 and second radial maximum or limit 512 maybe overall diameter 508. Overall diameter 508 may be adjustable. Forexample, in deployed state 302, overall diameter 508 may be adjusted byrotating the pair of proximal locations 204, 206 relative to distalintersection 208. More particularly, distal intersection 208 and/or adistal surface of the outer envelope of splines 202 may be pressedagainst an endocardial surface to fix distal intersection 208 relativeto the endocardial surface. Catheter shaft 106 may be rotated, e.g., byrotating handle 108 about central axis 110, and thus the pair ofproximal locations 204, 206 coupled to distal end 114 of catheter shaft106 may rotate about central axis 110 relative to distal intersection208. Rotation of the pair of proximal locations may twist splines 202around central axis 110 and cause splines 202 to wind around centralaxis 110. As splines 202 wind up, overall diameter 508 may decrease.Similarly, when splines 202 are twisted in an opposite direction thatcause splines 202 to unwind in an opposite direction about central axis110, overall diameter 508 may increase. Accordingly, overall diameter508 may be controlled to cause splines 202 to expand or contract.Expanding splines 202 can move electrodes 304 mounted on the splinesoutward against the endocardium. For example, electrodes 304 on spline202 at first radial limit 510 and second radial limit 512 may separatefrom each other and contact tissue on opposite sides of a heart chamber.Contracting splines 202 can move electrodes 304 inward from theendocardium for retrieval into catheter shaft 106.

Referring to FIG. 6, a cross-sectional view, taken about line B-B ofFIG. 3, of several splines of an expandable member symmetricallyarranged about a central axis is shown in accordance with an embodiment.Each spline 202 may be symmetrically disposed about central axis 110 atdistal end 114 of catheter shaft 106. For example, cross-sectional areasof splines 202 at a point where splines 202 enter into the inner lumenof catheter shaft 106 may be arranged circumferentially about centralaxis 110. The cross-sectional areas around central axis 110 may bespaced apart from each other equally. That is, a peripheral angle 602separating a radial axis 604 extending from central axis 110 through afirst cross-sectional area and a radial axis 604 extending from centralaxis 110 through a second cross-sectional area may equal 360° divided bythe number of spline 202 cross-sectional areas at distal end 114 ofcatheter shaft 106. More particularly, when eight cross-sectional areasare present at distal end 114, peripheral angle 602 between eachadjacent spline may equal 45°. Expandable member 104 may have between3-24 splines 202, and thus, between 6-48 spline segments andcorresponding axes 604 at distal intersection 208, although this isoffered by way of example only and not by way of limitation

In an embodiment, expandable member 104 is formed from a shape memorymaterial. For example, splines 202 may be drawn Nitinol wire. During afabrication process, the splines 202 may be heat set in a predeterminedconfiguration. For example, each spline 202 may have a cross-sectionalarea of a particular shape, e.g., rectoval (FIG. 13). Thecross-sectional area may have a width and a height, and the width may begreater than the height. Width may be at least twice height, e.g., widthmay be 0.015 inch and height may be 0.005 inch. Furthermore, thecross-sectional profile may be tilted relative to central axis 110. Forexample, a peripheral axis 606 extending parallel to a width of thespline cross-sectional area may not be orthogonal to a correspondingradial axis 604. That is, peripheral axis 606 may be oblique to thecorresponding radial axis 604. The tilted profile of spline 202 mayresist bending under compressive loads from a surrounding anatomy.Accordingly, cross-sectional areas of splines 202 arranged in a pinwheelfashion may improve stability of the overall structure of expandablemember 104.

Each spline 202 of expandable member 104 may twist around central axis110 between the proximal location at distal end 114 of catheter shaft106 and distal intersection 208. That is, spline 202 may extend betweenthe proximal location (204 or 206) and distal intersection 208 along apath that has both an axial component and a peripheral component (e.g.,circumferentially around central axis 110). FIGS. 7A-7D illustrate topviews, which reveal a top-down profile of a single spline 202 of anexpandable member 104 exhibiting different degrees of twist aboutcentral axis 110 in accordance with several embodiments.

Referring to FIG. 7A, spline 202, which may extend continuously fromproximal location 204 to proximal location 206, can be segmented forpurposes of description. Spline 202 extending between first proximallocation 204 and second proximal location 206 through distalintersection 208 may have a top-down profile resembling a figure-eight.Accordingly, first spline segment 402 extending between first proximallocation 204 and distal intersection 208 may have a top-down profileresembling half of a figure-eight. First spline segment 402 may be acircuitous path, such as a loop, extending away from and returning tocentral axis 110. The top-down profile of first spline segment 402 maybe further segmented. For example, the circuitous path of first splinesegment 402 may have one or more subsegments exhibiting top-downprofiles that are straight and one or more subsegments exhibitingtop-down profiles that are curved. The straight and curved profilesubsegments may be interconnected to form the continuous circuitous pathlooping outward and back to central axis 110.

A first subsegment 702 of first spline segment 402 may have a firsttop-down profile extending straight between central axis 110 and asecond subsegment 704 of first spline segment 402. More particularly,first subsegment 702 may extend along a path, which when viewed fromabove, is linear and in a first radial direction 708. First subsegment702 may join second subsegment 704 at a distal subsegment end 706 ofsecond subsegment 704. Distal subsegment end 706 may be aligned withcentral axis 110 in first radial direction 708.

Second subsegment 704 of first spline segment 402 may have a secondtop-down profile curving between first subsegment 702 and a proximalsubsegment end 710. More particularly, second subsegment 704 may extendalong a curvilinear path between distal subsegment end 706 and proximalsubsegment end 710. The curvilinear path, when viewed from above, may begenerally c-shaped. In perspective, however, the curvilinear path mayspiral about central axis 110 between a radially outward end of firstsubsegment 702, and a radially outward end of a third subsegment 712(FIG. 4).

Third subsegment 712 of first spline segment 402 may have a thirdtop-down profile extending straight between proximal subsegment end 710of second subsegment 704, and central axis 110. More particularly, thirdsubsegment 712 may extend along a path, which when viewed from above, islinear and in a second radial direction 714. The segment profile ofthird subsegment 712 may extend along longitudinal plane 502 fromproximal subsegment end 710 to central axis 110 continuously withinlongitudinal plane 502. Accordingly, proximal subsegment end 710 may bealigned with central axis 110 in second radial direction 714.

The spline segments may be joined at distal intersection 208.Accordingly, first spline segment 402 may spiral about central axis 110on first side 504 of longitudinal plane 502, and second spline segment404 may spiral about central axis 110 on second side 506 of longitudinalplane 502. Spiraling of the subsegments, however, may be limited to thearcuate portions of spline 202, e.g., second subsegment 704.

Both first spline segment 402 and second spline segment 404 may includeportions of first spline subsegment 702 having a top-down profile thatextend straight and/or orthogonal to the longitudinal plane 502. In anembodiment, spline 202 includes a fourth subsegment 718 on second side506 of longitudinal plane 502, opposite from second subsegment 704.Longitudinal plane 502 may be a plane of symmetry dividing secondsubsegment 704 and fourth subsegment 718. That is, fourth subsegment 718may form an arc of a half figure-eight profile opposite from the halffigure-eight profile of second subsegment 704. Fourth subsegment 718 mayspiral about central axis 110 with a different rotational clocking thansecond subsegment 704. For example, second subsegment 704 may spiralabout central axis 110 in a clockwise direction, and fourth subsegment718 may spiral about central axis 110 in a counterclockwise direction. Aform of second subsegment 704 may be geometrically transformed into theform of fourth subsegment 718 by rotating second subsegment 704 aboutcentral axis 110 by a rotational angle of 180°.

The top-down profile of first subsegment 702 may extend straight betweensecond subsegment 704 and fourth subsegment 718. For example, fourthsubsegment 718 may have a subsegment end 719 mirroring distal subsegmentend 706 about longitudinal plane 502. First subsegment 702 may extendbetween distal subsegment end 706 of second subsegment 704 andsubsegment end 719 of fourth subsegment 718.

In an embodiment, an angle 716 between longitudinal planes within whichfirst subsegment 702 and third subsegment 712 respectively extenddetermines a degree of twist of first spline segment 402 about centralaxis 110. The top-down profile of first subsegment 702 and the top-downprofile of third subsegment 712 may extend in respective radialdirections from central axis 110, and the radial directions may beseparated by angle 716. By way of example, angle 716 may be in a rangeof 70-200°. Still referring to FIG. 7A, angle 716 may be nominally 90°,and may vary within manufacturing tolerances of +/−20°. Accordingly,first spline segment 402 may extend from first proximal location 204 todistal intersection 208 over a quarter twist about central axis 110.Second segment 404 may be symmetric relative to first segment 402, andthus, a twist angle of second segment 404 may be similarly determined.The term symmetric here describes a rotation symmetry between secondsegment 404 and first segment 402. That is, the form of first segment402 may be rotated about central axis 110 over an angle of 180° tocoincide with the form of second segment 404.

It will be appreciated that the twist of the splines about central axis110 may be defined or modified in manners other than adjusting angle716. For example, angle 716 may be 90° as defined above, however, thetransition from first subsegment 702 or third subsegment 712 to secondsubsegment 704 may differ from the example illustrated in FIG. 7A. Thatis, the transition may not be smooth, but may instead be angled.Furthermore, the profile of second subsegment may not follow acontinuous arc between first subsegment 702 and third subsegment 712,but may instead undulate or otherwise advance along the envelope definedby the expandable member 104. In short, the embodiments illustrated inFIG. 7A-7D are illustrative and are not be considered limiting of otherspline profiles that may be contemplated by one skilled in the art.

The twist angle of the spline segments may be different in otherembodiments. Referring to FIG. 7B, first subsegment 702 may extend infirst radial direction 708 away from central axis 110, and thirdsubsegment 712 may extend in second radial direction 714 away fromcentral axis 110. The longitudinal planes within which first subsegment702 and third subsegment 712 are contained (and within which centralaxis 110 is contained) may be spaced apart by angle 716 of about 135°.For example, angle 716 between the top-down profiles of first subsegment702 and third subsegment 712 may be in a range of 115-155°.

Referring to FIG. 7C, first subsegment 702 may extend in first radialdirection 708 away from central axis 110, and third subsegment 712 mayextend in second radial direction 714 away from central axis 110. Theradial directions may be opposite directions from one another. That is,the longitudinal planes within which first subsegment 702 and thirdsubsegment 712 are contained may be spaced apart by angle 716 of about180°. For example, angle 716 between the top-down profiles of firstsubsegment 702 and third subsegment 712 may be in a range of 160-200°.

The degree of twist of spline segments about central axis 110 maydetermine different levels of chamber wall apposition of electrodes 304and/or structural stability of expandable member 104. As describedabove, expandable member 104 can include one or more electrodes 304mounted on an outward facing surface of spline 202. For example,electrodes 304 may be mounted on second subsegment 704 of spline 202along the curvilinear path radially outward from central axis 110. In anembodiment, angle 716 determines a pitch angle of spline 202 relative toa transverse plane, and accordingly, angle 716 determines a density ofelectrodes 304 in contact with an endocardium. Increasing angle 716 mayincrease an amount of the outer surface area of spline 202 that contactsthe endocardium, and thus, may increase a density of electrode contact.For example, a distance between the proximal location and the distallocation of spline 202 may be longer for larger angles 716, which canresult in more electrodes 304 in contact with endocardium. Accordingly,angle 716 may be tuned to achieve an amount of apposition betweenelectrodes 304 on spline 202 and the endocardium. Angle 716 may alsoaffect a resilience of expandable member 104. For example, smallerangles 716 may cause splines 202 to be more axially aligned thancircumferentially aligned relative to the heart chamber, and thus,smaller angles 716 may create stiffer and more robust structures.Accordingly, angle 716 may be tuned to achieve a balance betweenelectrode apposition and structural rigidity.

Referring to FIG. 7D, structural rigidity may be further tuned byintroducing local bends in the subsegments of spline 202. For example,second subsegment 704, which extends between distal subsegment end 706and proximal subsegment end 710, may include one or more undulations720. Undulations 720 may be localized bends or curvatures havingdifferent radii than surrounding portions of second subsegment 704. Forexample, undulation 720 may be located along second subsegment 704between a first subsegment portion 722 and a second subsegment portion724. First subsegment portion 722 and second subsegment portion 724 mayhave radii measured from longitudinal axes on a first side of secondsubsegment 704, e.g., within the loop circumscribed by the top-downprofile of second subsegment 704. Undulation 720 may have a radiusmeasured from a longitudinal axis on a second side of second subsegment704, e.g., outside of the loop circumscribed by the top-down profile ofsecond subsegment 704. Thus, undulation 720 may have an inflection pointat which first subsegment portion 722 transitions into second subsegmentportion 724. Undulations 720 may be included at various locations alongsecond subsegment 704 to create different rates of load bearingthroughout spline 202. Spline 202 may therefore resist forces applied bythe endocardium in different directions and be less susceptible tocrushing. That is, undulations 720 may increase a structural stabilityof expandable member 104.

Referring to FIG. 8, a perspective view of a spline of an expandablemember exhibiting a twist about a central axis is shown in accordancewith an embodiment. The perspective view shows spline 202 in deployedstate 302, and having spline segments that twist about central axis 110over a 90° angle 716. As described above, angle 716 may vary, and thus,the following description may be applicable to spline twisting ofvarious degrees. In an embodiment, first subsegment 702 intersectscentral axis 110 at distal intersection 208. First subsegment 702 mayextend through central axis 110 from second subsegment 704 on first side504 of longitudinal plane 502 to fourth subsegment 718 on second side506 of longitudinal plane 502. Similarly, first spline segment 402 andsecond spline segment 404 may meet central axis 110 at a proximalintersection 802, e.g., at proximal locations of expandable member 104.For example, third subsegment 712 of first spline segment 402 may extendradially inward toward central axis 110 from proximal subsegment end 710to proximal intersection 802. Third subsegment 712 may be considered tointersect central axis 110 at proximal intersection 802 even when thirdsubsegment 712 and central axis 110 do not actually coincide at a point.More particularly, in an embodiment, spline subsegments running throughthe inner lumen of catheter shaft 106 may be symmetrically disposedabout central axis 110 and separated from each other by a spline gap804. That is, each spline subsegment within the inner lumen may beseparated from an adjacent spline subsegment by an equal angle aboutcentral axis 110. Spline gap 804 may be small, e.g., on an order of onemillimeter, and thus the spline subsegments may never actually coincidewith central axis 110 that runs between them. Nonetheless, for thepurposes of understanding, spline 202 may be considered as intersectingcentral axis 110 at the pair of proximal locations and/or at distal end114 of catheter shaft 106.

Similar to the lateral separation between proximal locations 204, 206 ofspline 202, the pair of proximal locations may be axially separated froma distal location of spline 202. More particularly, proximalintersection 802 may be separated from distal intersection 208 alongcentral axis 110. The space between distal intersection 208 and proximalintersection 802 may be referred to as an axial gap 806. Axial gap 806may be distinguished from, e.g., a central shaft interconnecting aproximal portion and a distal portion of an expandable basket. Moreparticularly, distal intersection 208 and proximal intersection 802 maybe separated by a space and allowed to float relative to each other.Distal intersection 208 and proximal intersection 802 of spline 202 maybe connected only by the spline segments twisting outward and aroundcentral axis 110. A lack of a central shaft can allow the tip ofexpandable member 104 at distal intersection 208 to float freelyrelative to a base of expandable member 104 attached to catheter shaft106 at proximal intersection 802. The floating tip may therefore adjustto anatomical variations more readily, and expandable member 104 mayresultantly include greater structural resilience than an expandablebasket having a central shaft throughout the basket length.

Referring to FIG. 9, a side view of a spline of an expandable memberexhibiting a twist about a central axis is shown in accordance with anembodiment. The side view is for a spline having a spline segmenttwisting 90° about central axis 110, but the illustrated aspects areapplicable to the other spline configurations described above. The sideview shows that first subsegment 702 may have a side profile that is notstraight between second subsegment 704 and fourth subsegment 718. Firstsubsegment 702 may be bowed. First subsegment 702 of spline 202 may bean arcuate spline segment 902 having a side profile that curves within alongitudinal plane containing central axis 110. It will be appreciatedthat arcuate spline segment 902 may extend from distal subsegment end706 of second subsegment 704 through central axis 110 to subsegment end719 of fourth subsegment 718. Thus, a central portion of arcuate splinesegment 902 may be at a different axial height along central axis 110than the radially outward ends of arcuate spline segment 902.

In an embodiment, first spline segment 402 has a first distalmostlocation 904 on first side 504 of longitudinal plane 502, and secondspline segment 404 has a second distalmost location 906 on second side506 of longitudinal plane 502. First distalmost location 904 may or maynot be at the distal subsegment end 719, and second distalmost location906 may or may not be at subsegment end 719. That is, the distalmostlocations are at the most distal points on spline 202 regardless ofwhether the points are on a particular subsegment based on thesubsegment profile definitions described above.

Referring to FIG. 10, a side view, which reveals a side profile of adistal portion of an expanded spline of an expandable member is shown inaccordance with an embodiment. The distalmost locations of spline 202may be distal to distal intersection 208 in deployed state 302. Forexample, arcuate spline segment 902 may extend from first distalmostlocation 904 to second distalmost location 906 through distalintersection 208, and distal intersection 208 may be nearer to cathetershaft 106 than the distalmost locations. Thus, first subsegment 702 mayhave a bowed side profile. Alternatively, distalmost locations anddistal intersection 208 may be arranged at a same axial distance fromcatheter shaft 106 in deployed state 302. For example, as shown by thedashed line in FIG. 10, first subsegment 702 may have a side profileextending straight between first distalmost location 904 and seconddistalmost location 906. Accordingly, the radially oriented subsegmentmay extend within a transverse plane containing both distal intersection208 and the distalmost locations 904, 906. In deployed state 302therefore, distal intersection 208 may be axially aligned with orproximal to distal subsegment end 719.

Whether first subsegment 702 has a straight or arcuate side profile,spline 202 extends in transverse direction 306 from central axis 110 tothe distalmost locations 904, 906. Transverse direction 306, however,may have a radial component 1002 and/or an axial component 1004. Radialcomponent 1002 may be a component of transverse direction 306 orthogonalto central axis 110 at distal intersection 208. More particularly, aline drawn tangent to first subsegment 702 at distal intersection 208may have a component that extends radially away from central axis 110.Axial component 1004, on the other hand, may be a component oftransverse direction 306 parallel to central axis 110 at distalintersection 208. More particularly, the line drawn tangent to firstsubsegment 702 at distal intersection 208 may have a component thatextends along central axis 110. When the line drawn tangent to firstsubsegment 702 at distal intersection 208 includes both radial component1002 and axial component 1004, transverse direction 306 is oblique tocentral axis 110. On the other hand, when the line drawn tangent tofirst subsegment 702 at distal intersection 208 extends in transversedirection 306 having only radial component 1002, transverse direction306 is orthogonal to central axis 110, i.e., radiates from central axis110.

Spline 202 may have a concavity 1006 in one or both of deployed state302 or undeployed state 200. For example, arcuate spline segment 902having distalmost locations 904, 906 distal to distal intersection 208may have concavity 1006 that bows in an axial direction. Concavity 1006may include an apex 1008 on central axis 110 at distal intersection 208.Apex 1008 may be proximal to distalmost locations 904, 906 whenconcavity 1006 is concave upward (FIG. 10). Thus, in an embodiment,concavity 1006 is concave upward in deployed state 302.

A concave upward concavity 1006 can provide an atraumatic tip toexpandable member 104. That is, since distalmost locations 904, 906 areaxially offset from distal intersection 208, the distal intersection 208may be offset from endocardial tissue in deployed state 302.Furthermore, arcuate spline segment 902 can be flexible such that thedistal portion of expandable member 104 is resilient when pressedforward against tissue. The resilience can reduce a likelihood ofcausing tissue damage during manipulation of the expandable member 104,and thus, arcuate spline segment 902 provides an atraumatic tip forexpandable member 104 in deployed state 302.

Arcuate spline segment 902 can provide a spring force acting in atransverse direction on second subsegment 704 and fourth subsegment 718.For example, subsegment ends 706, 719 may connect to respective ends ofarcuate spline segment 902, and the respective ends may resist radialforces applied to subsegments 704, 718 by a surrounding endocardialtissue. Accordingly, arcuate spline segment 902 can increase a radialstiffness of expandable member 104 in deployed state 302. The radialstiffness of expandable member 104 having arcuate spline segment 902with a curved side profile may be greater than a radial stiffness ofexpandable member 104 having first subsegment 702 with a straight sideprofile, as indicated by the dashed line.

Expandable member 104 may also include a concavity near proximal ends204, 206 (not shown). For example, third subsegment 712 may curve in adistal direction from proximal subsegment end 710 to proximal end 206.That is proximal subsegment end 710 may be more proximal than proximalend 206. Accordingly, a proximal portion of expandable member 104 mayhave a concave downward configuration forming a dimple at the proximalregion of the envelope formed by expandable member 104.

Referring to FIG. 11, a side view of a distal portion of an unexpandedspline of an expandable member is shown in accordance with anembodiment. Apex 1008 may be distal to subsegment ends 706, 719 whenconcavity 1006 is concave downward. More particularly, apex 1008 atdistal intersection 208 along central axis 110 may be a distalmostlocation of spline 202 when spline 202 is constrained within, or in theprocess of deploying from, introducer 201. Distal intersection 208 maytherefore be distal to distal subsegment end 706 and/or subsegment end719 in undeployed state 200. Accordingly, first subsegment 702 may bebowed with concavity 1006 being concave downward in undeployed state200.

Referring to FIG. 12, a side view of a spline of an expandable memberhaving portions of varying radiopacity is shown in accordance with anembodiment. In addition to defining segments and subsegments of spline202 based on top-down and side profiles, spline portions may be definedaccording to relative radiopacity. For example, a first portion 1202 offirst spline segment 402 may have a first radiopacity, and a secondportion 1204 of first spline segment 402 may have a second radiopacity.The radiopacity of first portion 1202 may be different than theradiopacity of second portion 1204. For example, first portion 1202 maybe more radiopaque than second portion 1204 (as indicated by the varyingline thickness). The difference in radiopacity between first portion1202 and second portion 1204 can indicate to a physician a relativeplacement of the portions within a target anatomy. For example, whenfirst portion 1202 is distal to second portion 1204, a physician mayrecognize first portion 1202 as a darker image on a fluoroscope, and maytherefore determine a relative placement of expandable member 104 withinthe target anatomy.

In an embodiment, portions of differing radiopacity may correspond tothe subsegments described above. For example, second subsegment 704and/or fourth subsegment 718 may have equivalent radiopacities. Bycontrast, the radiopacities of second subsegment 704 and/or fourthsubsegment 718 may differ from a radiopacity of first subsegment 702 orthird subsegment 712. As a result, both the subsegment profiles andsubsegment densities may provide to an observer indications of anorientation of expandable member 104 within the target anatomy.

Radiopacity of the spline portions may be tuned. For example, metallicradiomarkers may be added to spline 202 to vary radiopacity. A material,size, or density of spline 202 may also be varied to achieve a desiredradiopacity. By way of example, first portion 1202 may be doped withradiopaque filler to increase a respective radiopacity relative tosecond portion 1204. Other manners of tuning radiopacity are known inthe art.

Referring to FIG. 13, a cross-sectional view, taken about line C-C ofFIG. 12, of a spline of an expandable member is shown in accordance withan embodiment. Spline 202 may have a cross-sectional profile 1302 of agiven shape. As described above, cross-sectional profile 1302 may have awidth 1304 and a height 1306. Width 1304 and height 1306 may be equal,e.g., in the case of a square or a circular cross-sectional profile1302. Alternatively, width 1304 may be greater than height 1306, e.g.,in the case of an elliptical cross-sectional profile 1302.Cross-sectional area may include at least one flat side facing outwardtoward an endocardium in deployed state 302. For example,cross-sectional area may be an oval, triangle, flattened circle, orrectangle having a flattened surface facing outward. Cross-sectionalprofile 1302 may vary over a length of spline 202. For example,cross-sectional profile 1302 may have a first orientation relative to anaxial axis 1308 of spline 202, as illustrated in FIG. 13, and at adifferent location along spline 202 cross-sectional profile 1302 mayhave a different second rotational orientation relative to axial axis1308. Width 1304 may be horizontal in the first orientation, andvertical in the second orientation, relative to axial axis 1308.Accordingly, cross-sectional profile 1302 may revolve about axial axis1308 along the length of spline 202.

In an embodiment, the orientation of cross-sectional profile 1302relative to axial axis 1308 may vary along the length of spline 202 toachieve a predetermined relationship between portions of spline 202 anda surrounding environment. For example, cross-sectional profile 1302 mayhave an outward facing flat surface, and cross-sectional profile 1302may twist about axial axis 1308 to face the outward facing flat surfacetoward endocardial tissue when expandable member 104 is in deployedstate 302. In an embodiment, a radial vector radiating from a midpointon central axis 110 half of a distance between the proximal location 114and the distal intersection 208 passes orthogonal to the axial axis 110and the outward surface. Accordingly, the outward facing flat surfacefaces radially outward from the midpoint, which may be located near acentral point of an atrium in deployed state 302. Electrodes 304 may bemounted on the outward facing flat surface of cross-sectional profile1302, and thus, electrodes 304 may be in contact with the endocardialtissue to sense electrical activity in deployed state 302.

In an embodiment, cross-sectional profile 1302 of spline 202 isrectoval. The term rectoval is used to describe a profile having agenerally rectangular shape with rounded corners. As such,cross-sectional profile 1302 may include flat outer surfaces 1310 onopposite sides of axial axis 1308, and the outer surfaces 1310 may beconnected by sidewalls 1312 extending between the outer surfaces 1310.Sidewalls 1312 may have radii and/or may include chamfers or fillets atcorners where sidewalls 1312 transition into outer surfaces 1310. Therectoval, or ribbon-shaped, cross-sectional area may allow an electrode304 to reside on an outward facing (tissue contacting) surface of spline202. The shape may provide stability of splines 202 when contactingendocardial tissue. Such stability can prevent crushing or collapse ofexpandable member 104.

Referring to FIG. 14, a perspective view of an outer envelope of anexpandable member is shown in accordance with an embodiment. Examples ofseveral splines 202 are shown to convey that an outer envelope 1402 is ageometrical form representing a three-dimensional surface correspondingto a revolved surface of spline 1404 rotated about central axis 110 by360°. That is, outer envelope 1402 corresponds to a revolved surfaceformed by revolving spline 1404, however, a similar surface with aslightly different profile could be formed by revolving another examplespline 202. In either case, outer envelope 1402 can include a dimple1406 around distal intersection 208. Dimple 1406 corresponds toconcavity 1006 of the side profile of spline 202 (FIG. 10). As describedabove, a similar dimple may exist at a proximal region of the envelope(not shown). Dimple 1406 can include a curved depression in a surfacethat transitions smoothly from a generally spherical outer surface ofexpandable member 104 to an indentation near apex 1008. The transitionarea between the spherical outer surface and the distal concavityprovides an atraumatic outer envelope for expandable member 104.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications may be made thereto without departing fromthe broader spirit and scope of the invention as set forth in thefollowing claims. The specification and drawings are, accordingly, to beregarded in an illustrative sense rather than a restrictive sense.

What is claimed is:
 1. An expandable member, comprising: a splineincluding a first subsegment and a second subsegment, wherein the firstsubsegment, when viewed in an axial direction along a central axis,extends along a linear path in a radial direction between a distalintersection at the central axis and a distal subsegment end of thesecond subsegment, and wherein the second subsegment, when viewed in theaxial direction along the central axis, undulates along a curvilinearpath between the distal subsegment end and a proximal subsegment end ofthe second subsegment.
 2. The expandable member of claim 1, wherein thesecond subsegment undulates about the central axis along the curvilinearpath.
 3. The expandable member of claim 2, wherein the second subsegmentundulates continuously.
 4. The expandable member of claim 1, wherein thespline includes a third subsegment, and wherein a third top-down profileof the third subsegment viewed in the axial direction along the centralaxis is straight between the proximal subsegment end of the secondsubsegment and the central axis.
 5. The expandable member of claim 1further comprising a reference electrode mounted on anon-tissue-contacting surface of the expandable member.
 6. Theexpandable member of claim 1, wherein the expandable member has aspherical envelope including one or more of a concave pole or aflattened pole.
 7. The expandable member of claim 1, wherein the distalintersection is axially aligned with the distal subsegment end.
 8. Theexpandable member of claim 1, wherein the distal intersection isproximal to the distal subsegment end.
 9. The expandable member of claim1, wherein a first portion of the spline has a different radiopacitythan a second portion of the spline.
 10. An electrophysiology catheter,comprising: a catheter shaft extending along a central axis between aproximal end and a distal end; and an expandable member mounted on thedistal end, the expandable member including a spline including a firstsubsegment and a second subsegment, wherein the first subsegment, whenviewed in an axial direction along the central axis, extends along alinear path in a radial direction between a distal intersection at thecentral axis and a distal subsegment end of the second subsegment, andwherein the second subsegment, when viewed in the axial direction alongthe central axis, undulates along a curvilinear path between the distalsubsegment end and a proximal subsegment end of the second subsegment.11. The electrophysiology catheter of claim 10, wherein the secondsubsegment undulates about the central axis along the curvilinear path.12. The electrophysiology catheter of claim 10, wherein the splineincludes a third subsegment, wherein a third top-down profile of thethird subsegment viewed in the axial direction along the central axis isstraight between the proximal subsegment end of the second subsegmentand the central axis.
 13. The electrophysiology catheter of claim 10further comprising a reference electrode mounted on anon-tissue-contacting surface of the expandable member.
 14. Theelectrophysiology catheter of claim 10, wherein a first portion of thespline has a different radiopacity than a second portion of the spline.15. An electrophysiology catheter system, comprising: a catheter shaftextending along a central axis between a proximal end and a distal end;an expandable member mounted on the distal end, the expandable memberincluding a spline including a first subsegment and a second subsegment,wherein the first subsegment, when viewed in an axial direction alongthe central axis, extends along a linear path in a radial directionbetween a distal intersection at the central axis and a distalsubsegment end of the second subsegment, and wherein the secondsubsegment, when viewed in the axial direction along the central axis,undulates along a curvilinear path between the distal subsegment end anda proximal subsegment end of the second subsegment; and a handle coupledto the proximal end of the catheter shaft.
 16. The electrophysiologycatheter system of claim 15, wherein the second subsegment undulatesabout the central axis along the curvilinear path.
 17. Theelectrophysiology catheter system of claim 15, wherein the splineincludes a third subsegment, wherein a third top-down profile of thethird subsegment viewed in the axial direction along the central axis isstraight between the proximal subsegment end of the second subsegmentand the central axis.
 18. The electrophysiology catheter system of claim15 further comprising a reference electrode mounted on anon-tissue-contacting surface of the expandable member.
 19. Theelectrophysiology catheter system of claim 15, wherein a first portionof the spline has a different radiopacity than a second portion of thespline.
 20. The electrophysiology catheter system of claim 15 furthercomprising: an electrode on the spline; and a reference electrode on thecatheter shaft.